An optimal scaffold based strategy for in vivo repair of large bone defects and its associated problems is presented in this work. Three polymeric scaffolds produced by using an extrusion-based additive manufacturing system were examined in a rat critical bone defect model: scaffolds without cells, with undifferentiated Adipose-derived mesenchymal stem cells (ADSCs) and differentiated ADSCs (osteoblasts). Scaffolds with undifferentiated cells seem to be the best strategy as they exhibited around 22% more bone formation than natural bone healing, and around 15% more than the two other cases.Authors observed that scaffolds enabled cell migration and tissue formation. Results suggest that undifferentiated ADSCs strongly contribute to new bone formation with no rejection if scaffolds are used to support cell migration, proliferation and differentiation. Our long-term goal is to engineer high-quality cell seeded-scaffolds (autograft and allograft) for bone regeneration, mainly in elderly patients.